District of Columbia: The US Supreme Court on Wednesday appeared receptive to defense arguments that a 53-year-old death row inmate was sentenced to die two decades ago because he is African American.

Incarcerated in Texas, Duane Buck could be executed due to a conviction based in part on a psychologist`s testimony in the 1997 trial that he presented a higher risk of committing violent crimes because he was black.

Buck is appealing the death sentence, although his guilt is not at issue -- he was convicted of the brutal 1995 shooting deaths of his former lover and the man who was with her.

"This is a... very unusual case, and what occurred at the penalty phase of this trial is indefensible," said Samuel Alito, one of the eight Supreme Court justices hearing the case.

Several other justices expressed surprise that the state of Texas continues to refuse Buck`s requests for a new trial.

"Is there some good reason why this person shouldn`t have been able to reopen his case?" said Stephen Breyer, pushing the lawyer representing Texas.

The Supreme Court`s hearing of the case Wednesday comes amid an intense national debate over racism in law enforcement after a wave of police killings of black suspects.

Sentenced in Texas`s Harris County, where nine percent of all US executions occur, a record in the country, Buck has become another symbol of a judicial system seen as tinged with racial bias.Buck`s defense lawyers included Christina Swarns of the NAACP, the nation`s leading black civil-rights group, whose appearance Wednesday before the highest US court was in itself something of an event.

It is rare for an African-American attorney, and a woman at that, to present oral arguments to the justices -- of whom only one is African American.

"It is impossible to un-ring the bell," Swarns said of Buck`s case -- and the "explicit appeal to racial bias" that she said factored into his conviction.

According to Texas law, Swarns noted, a person can only be condemned to die if the prosecutor can prove he or she represents a future danger to society.

The testimony of psychologist Walter Quijano, who claimed that Buck was a high risk for recidivism because he was black, "put the thumb heavily on the death scale," she said.

Her adversary, Texas Solicitor General Scott Keller, focused his arguments on the fact that the psychologist had been presented as a witness by Buck`s defense lawyer himself.

"In the context of a prosecutor offering the testimony and using it as an aggravator, that would be an equal protection and due process violation," Keller said, pointing out the state was not responsible for errors committed by Buck`s attorney.

But Justice Ruth Bader Ginsburg took issue with that.

"I don`t know why it should make a difference that the petitioner`s counsel introduced this evidence. This evidence, everyone agrees, should not have -- not have come in," Ginsburg said.

At the time of his conviction, Buck was represented by two court-appointed lawyers. One of them, Jerry Guerinot, had won no acquittals over the course of his career and had no fewer than 20 clients who were sentenced to death.

The Supreme Court`s decision on the Buck appeal will come during its annual session that began Monday and will end in late June 2017.